The electrochemical interface between the lithium metal anode and the electrolyte in a lithium metal battery is stabilized by the use of a reactive polymer composite, enhancing the battery’s performance. Image: Donghai Wang, Penn State.Rechargeable lithium metal batteries with increased energy density, performance and safety may be possible thanks to a newly-developed solid-electrolyte interphase (SEI), according to researchers at Penn State.
As the demand for higher-energy-density lithium metal batteries increases – for use in electric vehicles, smartphones and drones – the stability of the SEI has been a critical issue hampering their development. The SEI is a salt layer that forms on the surface of the battery's lithium electrode, insulating the electrode and conducting lithium ions.
"This layer is very important and is naturally formed by the reaction between the lithium and the electrolyte in the battery," explained Donghai Wang, professor of mechanical and chemical engineering at Penn State. "But it doesn't behave very well, which causes a lot of problems."
The degradation of the SEI is one of the least-understood aspects of lithium metal batteries and contributes to the development of dendrites, which are needle-like formations that grow from the lithium electrode of the battery and negatively affect performance and safety. The researchers published their novel approach to this problem in a paper in Nature Materials.
"This is why lithium metal batteries don't last longer – the interphase grows and it's not stable," Wang said. "In this project, we used a polymer composite to create a much better SEI."
Led by chemistry doctoral student Yue Gao, the enhanced SEI is a reactive polymer composite consisting of a polymeric lithium salt, lithium fluoride nanoparticles and graphene oxide sheets. The composite is made up of thin layers of these materials, which is where Thomas Mallouk, a professor of chemistry at Penn State, lent his expertise.
"There is a lot of molecular-level control that is needed to achieve a stable lithium interface," Mallouk said. "The polymer that Yue and Donghai designed reacts to make a claw-like bond to the lithium metal surface. It gives the lithium surface what it wants in a passive way so that it doesn't react with the molecules in the electrolyte. The nanosheets in the composite act as a mechanical barrier to prevent dendrites from forming from the lithium metal."
This collaboration between chemistry and engineering design allowed the researchers to control the lithium surface at the atomic scale. "When we engineer batteries, we don't necessarily think like chemists, all the way down to the molecular level, but that's what we needed to do here," said Mallouk.
The reactive polymer composite also reduces the weight and manufacturing cost, further enhancing the future of lithium metal batteries. "With a more stable SEI, it's possible to double the energy density of current batteries, while making them last longer and be safer," Wang said.
This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.